<template>
    <ul class="list">
       <li class="item" v-for="item of letters" 
       :key="item"
       :ref="item"
       @touchstart.prevent="handleTouchStart"
       @touchmove="handleTouchMove"
       @touchend="handleTouchEnd"
       @click="handleLetterClick"
       >
       {{item}}
       </li>
    </ul>
</template>

<script>
export default {
    name: 'CityAlphabet',
    props: {
        cities: Object
    },
    computed: {
        letters() {
            const letters = []
            for (let i in this.cities) {
                letters.push(i)
            }
            return letters
        }
    },
    data () {
        return {
            touchStatus:false,
            startY: 0,
            timer: null
        }
    },
    updated () {
        this.startY  = this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick (e) {
            this.$emit('change', e.target.innerText)
        },
        handleTouchStart () {
            this.touchStatus = true
        },
        handleTouchMove (e) {
            if (this.touchStatus) {
                if (this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout (()=>{
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    if (index >= 0 && index < this.letters.length){
                        this.$emit('change',this.letters[index])
                    }
                },16)
            }
        },
        handleTouchEnd () {
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
   @import '~styles/varibles.styl'
   .list
        display:flex 
        flex-direction:column
        justify-content:center
        position: absolute 
        right:0
        top:1.58rem 
        bottom:0 
        width:.4rem 
        .item
            line-height:.4rem
            text-align:center
            color:$bgColor
</style>
